In the commercial roofing industry, certain roofing systems are categorized as “single ply” membrane roofing systems. These roofing systems consist of roof membranes that are installed as a single layer. Exemplary membranes are made of ethylene propylene diene terpolymer (EDPM), PVC, thermoplastic polyolefin (TPO), chlorosulfonated polyethylene (CSPE), polyisobutylene (PIB), and modified bitumen. The roof membranes are generally installed by one of three methods: ballasted, mechanically attached, or adhered using adhesives. Generally, commercial roof membranes are installed over roof insulation. The insulation is typically a layer of rigid foam or fiberglass insulation material disposed between two facer layers made of, or are composites of, fiberglass, aluminum, wood, cellulose, paper or other building material. Typically, the roof membrane is attached to or disposed against the top facer layer of the insulation.
Single-ply roof membranes are typically manufactured as elongated sheets having typical widths ranging from approximately 1 to 3 meters or greater. The sheets are typically sold, transported, and stored in rolls. The sheets are unrolled at the installation site and cut and fit to the size of the intended application by piecing together multiple pieces of the membrane. During installation, the edges of adjacent pieces of the sheets are overlapped and sealed together. The sheets of roof membrane are typically held in place over roof insulation by means of stone ballast, mechanical attachment, or adhered to the roof insulation with an adhesive.
Typical adhesive systems used to seal, or seam, edges together or to seal the roof membrane to insulation (which may include one or more insulation facers) include contact or pressure sensitive adhesive compounds. Examples of such compounds include those formulated with neoprene, butyl or butyl type polymers, and tackifying olefins. Those compounds, however, often provide poor peel strength. Furthermore, they often experience degradation in seam performance at elevated temperatures. Other examples of pressure sensitive adhesive compositions for seaming roofing materials are disclosed in U.S. Pat. Nos. 3,801,531 and 3,867,247. However, these adhesive compositions suffer from poor adhesive properties and may contain organic solvents which may be prohibited by environmental regulations. Such adhesives are expensive and time-consuming to apply and are prone to delamination which may cause leaks or separation of the membrane from the insulation facers.
When an adhesive is used to adhere the roof membrane sheet to the roof insulation facer, the roof membrane is typically laid out and positioned over roof insulation, one-half of the roof membrane sheet is folded back onto itself and adhesive, typically packaged in five gallon pails, is applied to both the backside of the roof membrane and the roof insulation surface with long handled paint rollers. After adhesive set up, i.e., solvent flash off, the folded back membrane is rolled into place and the procedures repeated for the other half of the sheet. This method is somewhat similar to installing wallpaper on a flat surface. Adhesives used are typically solvated, water-based or two-part urethane type products.
When adhering roof membranes to surfaces such as insulation facers, there are a number of shortcomings associated with the use of adhesives, including: the lack of reliable bonds, condensation forming on the adhesive surface which inhibits bonding, environmental concerns associated with flash off of solvent carriers, landfill disposal concerns associated with the large quantities of adhesive buckets, and residual solvent from the contact adhesive becoming trapped between the roof membrane and insulation, causing delamination. These adhesive compositions often suffer from poor adhesive performance properties due to human application error, and may contain organic solvents which may be prohibited by environmental regulations.
In recent years, thermoplastic polyolefin compounds have been used increasingly in roof membrane applications due to factors such as low cost and environmental acceptance. Efforts have been undertaken to secure these thermoplastic olefin compound membranes in place by adhesives to adhere the membranes to insulation facers.
Thermoplastic membranes may include components in the membrane formulations designed to promote adhesion between adjoining membrane sheets. WO 02/051928 discloses a composite polymer structure in which a first polymer is adhered to and is in surface contact with a second polymer structure by adhesive interface between the first polymer structure and the second polymer structure. Interfacial adhesion is provided by a semi-crystalline random copolymer in the first polymer structure, in the second polymer structure, and in a third adhesive layer, if used.